MINOR: debug: also add a pointer to struct global to post_mortem

MINOR: debug: also add a pointer to struct global to post_mortem

The pointer to struct global is also an important element to have in
post_mortem given that it's used a lot to take decisions in the code.
Let's just add it. It's worth noting that we could get rid of argc/argv
at this point since they're also present in the global struct, but they
don't cost much there anyway.

(cherry picked from commit 2f04ebe14aca91f4a0fafcd03a0f310d98d97aaf)
Signed-off-by: Willy Tarreau <w@1wt.eu>